A typical cellular phone is capable of giving the user the melody of a song when an incoming call is received and also, transmitting an incoming voice signal to the user. The melody sound has a frequency of from 20 Hz to 20 kHz, whereas the voice sound has a frequency of from 300 Hz to 3 or 4 kHz. To this end, the cellular phone is generally provided with two different electric-acoustic transducers. To minimize the size of this kind of cellular phone, an attempt has been made to provide a single transducer assembly wherein two different transducers are integrated together.
FIG. 10 shows one example of a cellular phone with a single electric-acoustic transducer assembly. The cellular phone includes a housing 182 and an electric-acoustic transducer assembly 184 arranged within the housing 182. The electric-acoustic transducer assembly 184 includes a first vibratory plate 186, a second vibratory plate 190 and an exciter 198 disposed between the first and second vibratory plates 186, 190 and having a first and second exciter section 194, 196 integrally formed together and adapted to induce vibration of the first and second vibratory plates 186, 190. In this example, the first vibratory plate 186 and the first exciter section 194 collectively form a first transducer adapted to give the user the melody of a song upon receipt of an incoming call. Similarly, the second vibratory plate 190 and the second exciter section 196 collectively form a second transducer adapted to transmit an incoming voice signal to the user.
The electric-acoustic transducer assembly 184 includes a casing 200 within which the exciter 198, the first vibratory plate 186 and the second vibratory plate 190 are housed. The casing is composed of an annular member 202 and a top and bottom cover 204, 206 connected at their opposite ends to the annular members 202.
As shown, a first outer chamber 208 is defined between the top cover 204 and the first vibratory plate 186, and a second outer chamber 210 is defined between the bottom cover 206 and the second vibratory plate 190. Similarly, a first inner chamber 212 is defined between the exciter 198 and the first vibratory plate 186, and a second inner chamber 214 is defined between the exciter 198 and the second vibratory plate 190. The top and bottom covers 204, 206 include respective sound openings 208a, 210a through which the first and second outer chambers 208, 210 are communicated with the outside of the casing 200. Similarly, the annular members 202 include respective sound openings 212a, 214a through which the first and second inner chambers 212, 214 are communicated with the outside of the casing 200.
The housing 182 has a plurality cushioning elements 216, 218 to support the transducer assembly. The cushioning elements 216, 218 define two side chambers 220, 220 within the housing 182. The first and second inner chambers are communicated with one another through these two side chambers. A problem with this structure is that the first and second vibratory plates 186, 190 interfere with each other due to the sound pressure developed by themselves.
It is, therefore, an object of the present invention is to provide an electric-acoustic transducer and an electric-acoustic transducer/housing assembly which overcomes the problem encountered in the known electric-acoustic transducer.